1. Field of the Invention
The present invention relates generally to a dielectric filter having at least one dielectric resonator, the dielectric resonator having an internal conductor which is formed within a dielectric block and an external conductor which is formed on the outside of the dielectric block.
2. Description of Related Art
Filters for use in, for example, the microwave band, include a dielectric filter, in which a resonator electrode is formed within a dielectric block and an earth electrode is formed on the outside face of the dielectric block, and a so-called Triplate (TM) type of dielectric resonator with strip lines located opposite to each other on respective main faces of a dielectric substrate, the strip lines serving respectively as a signal strip line on one main face and an earth electrode on the other main face.
FIG. 39 shows an exploded perspective view of the construction of the conventional general dielectric resonator using a dielectric block. In FIG. 39, reference numeral 40 is a six-sided dielectric block with three internal conductor holes 46, 47, 48 each having an internal conductor provided therein and coupling holes 49, 50 which are provided between the internal conductor holes 46, 46, 48. The internal conductors are formed on the inside surfaces of the internal conductor holes 46, 47, 48, and an external conductor 51 is formed on five faces of the dielectric block 40 except for an open face 52. Reference numerals 53, 54 are so-called resin pins, each being composed of resin portions 53a, 54a and signal input, output terminals 53b, 54b. Two resin pins 53, 54 are inserted into the internal conductor holes 46, 48 from the open face side of the dielectric block 40 so that the terminals 53b, 54b are coupled capacitively to the corresponding internal conductors within the internal conductor holes 46, 48. Reference numeral 55 is a case for retaining the dielectric block 40 and the resin pins 53, 54 and also, for covering the open face portion of the dielectric block 40. The resin pins 53, 54 are respectively inserted into the dielectric block 40 so as to be covered by the case 55, and also, the whole arrangement is integrated by soldering the case 55 to the external conductor 51. For mounting the dielectric resonator on a circuit substrate, the projecting portions 55a, 55b of the case 55 function as an earth terminal.
As shown in FIG. 39, many components such as input, output terminals 53b, 54b, case 55 and so on, are necessary if a plurality of resonators are to be formed in a single dielectric block. The assembly steps therefore become complicated. Moreover, it is necessary to attach a lead wire to the component when mounting the completed product on a circuit substrate. Therefore, surface mounting cannot be effected, as it can with other electronic components, so as to mount a plurality of these completed products on the same circuit substrate. Thus, it is difficult to provide an assembly which is low in height.
Further, if the case 55 is not used, the external conductor 51 of the dielectric block 40 is directly connected to the earth electrode on the circuit substrate, so that the open face 52 is exposed, and thus, electromagnetic field leakage occurs at this location. Thus, when a metallic object approaches the open face 52, the metallic object influences this electromagnetic field. Further, since the resonator is coupled with this electromagnetic field, the desired characteristics of the dielectric resonator cannot be obtained.
Accordingly, the present invention has been developed with a view to substantially eliminating the above discussed drawbacks that are inherent in the prior art, and has for its essential object to provide an improved dielectric resonator.
Another important object of the present invention is to provide an improved dielectric resonator which can be surface mounted on the circuit substrate without the use of resin pins and a case as individual parts, as required by the prior art device shown in FIG. 39.
Still another object of the present invention is to provide a dielectric resonator in which electromagnetic field leakage between the inside and the outside of the resonator near the opening portion is reduced, so as to remove the problem caused by the above described electromagnetic field leakage.
A further object of the invention is to provide a method by which a resonator can be adjusted with ease and accuracy so as to have desired characteristics.
A further object of the present invention is to provide a dielectric resonator in which it is easier to obtain floating capacitance by a comparatively simple working or molding operation.
In accomplishing these and other objects, a dielectric resonator in accordance with a first aspect of the invention is provided having a non-conductive portion formed in at least one internal conductor near one end face of the above described dielectric block, and signal input, output electrodes for providing capacitive connection with the above described internal conductor are provided on the outer surface of the dielectric block. The dielectric resonator includes at least one internal conductor hole, or a plurality of internal conductor holes, within the dielectric block, the external conductor being formed on the outside of the above described dielectric block.
In the dielectric resonator of the first aspect of the invention, the non-conductive portion in the internal conductor hole is provided near one end face of the at least one hole, or the plurality of holes, of the dielectric resonator, and the signal input, output electrodes effect capacitive connection with the internal conductor. A tip end capacitance is created at the non-conductive portion in the at least one internal conductor hole so as to provide comb-line coupling or interdigital coupling between the adjacent resonators. In this construction, the conductor is not removed from either end face of the dielectric body, so that large electromagnetic field leakage is avoided.
As coupling holes are not required, the whole arrangement can easily be made smaller in size. As the signal input, output electrodes are provided so as to provide a capacitive connection with the internal conductor, the signal input, output terminals are not required to be separate, individual parts. The external conductor can be connected with the earth electrode on the circuit substrate by surface mounting, and also, the signal input, output electrodes can be similarly connected with the signal line on the circuit substrate.
A dielectric resonator of a fourth aspect of the invention has internal conductor holes in the dielectric block, each having an internal conductor formed on the inside surface thereof, an external conductor is provided on the outside face of the dielectric block, and hollows in at least one end face of the dielectric block are centered on the internal conductor holes, so that the internal conductors are removed near the above described hollows. Due to the hollows centered on the internal conductor holes in at least one end face of the dielectric block, the open-circuited ends of the internal conductors are formed at locations spaced from the end face, so that electromagnetic field leakage between the inside and the outside of the dielectric resonator is lessened and stable resonator characteristics are obtained.
In a dielectric resonator of a second aspect of the invention, the non-conductive portions in the internal conductor holes are formed by removing one portion of the internal conductor from a location near the end face of the dielectric block but spaced from the end face. In the dielectric resonator of the fifth aspect of the invention, as the non-conductive portion is spaced from the end face of the resonator, the electromagnetic field leakage is further reduced.
A dielectric resonator of a third aspect of the invention is made resonant at a desired frequency by forming a concave portion on the surface of the above described dielectric block so as to cause the outside conductor at the bottom portion of the concave portion to approach the above described internal conductor.
In the third aspect of the invention, since the outside conductor at the bottom portion of the concave portion formed on the surface of the dielectric block is bought towards the above described inside conductor, the interval becomes smaller between the internal conductor in the hole and the outside conductor, which serves as an earth electrode, whereby floating capacitance is obtained. The floating capacitance can be adjusted by a comparatively simple working or molding operation to fix the size, depth and so on of the concave portion. In the comb-line type resonator, the bandwidth of the filter can be made larger by provision of, for example, a larger floating capacitance. The resonator length becomes shorter, and the size can be made smaller by the provision of the larger floating capacitance.
In a characteristic adjusting method for a dielectric resonator, according to a fourth aspect of the invention, the resonator comprises a resonator hole with an internal conductor formed on its inside surface and with an external conductor being formed on the outside surface of the dielectric, the method comprising the steps of removing the internal conductor near an end of the resonator hole, for example by grinding, thereby adjusting the tip end capacitance between the internal conductor and the hollow.
In the above-described characteristic adjusting method, the internal conductor near one end face of the dielectric is removed. However, not all of the internal conductor formed extending inward into the resonator hole is removed when the internal conductor is removed near the end face. A selected portion of the internal conductor and the dielectric can be removed with high accuracy. As a result, the desired resonator characteristics can be obtained with ease, in a short time, and with high accuracy.
In a characteristic adjusting method for a dielectric resonator according to a fifth aspect of the invention, each of the plurality of resonator holes has an inner surface with a substantially constant cross-sectional shape along its axial direction and an internal conductor provided on the inner surface, a non-conductive portion being provided at the inner surface of the hole, a surface of the non-conductive portion being substantially flush with the inner surface of the hole, the method comprising the steps of initially forming each internal conductor over an entire length of the inner surface of the hole, and thereafter removing, for example by grinding, a portion of the inner conductor in order to form the non-conductive portion.
According to a sixth aspect of the invention, the characteristic adjusting method of the fifth aspect of the invention may comprise the additional step of forming the dielectric body with first and second portions on its outer surface which are spaced away from the hole by different respective distances.